diff --git a/lib/http.c b/lib/http.c
index 1f17b9c003e14685cf74270c7d4a7334b104d9f3..4984d684dde886ea4ffd9d4da62cb22c946a04f5 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -718,8 +718,7 @@ CURLcode Curl_http(struct connectdata *conn)
       http->storefread = data->fread; /* backup */
       http->in = data->in; /* backup */
           
-      data->fread =
-        (size_t (*)(char *, size_t, size_t, FILE *))
+      data->fread = (curl_read_callback)
         Curl_FormReader; /* set the read function to read from the
                             generated form data */
       data->in = (FILE *)&http->form;